Engineering of low germination stimulant production to control witchweed infection in maize in Sub-Saharan Africa

The parasitic witchweeds, such as Striga hermonthica and Striga asiatica, pose an enormous threat for production of cereal crops, such as sorghum, millet and maize, in the African continent, threatening the livelihood of millions of people, especially in sub-Saharan Africa.

Striga seeds lay dormant in the soil until their germination is triggered by strigolactones (SLs), signaling compounds exuded by roots of plants, including maize.

Maize exudes at least six different SLs from its roots into the rhizosphere, two of which were structurally identified as zealactone and zeapyranolactone.In work on maize strigolactone biosynthesis that was part of the ERC Advanced grant CHEMCOMRHIZO we demonstrated that there is natural variation in the germination stimulant composition in the root exudate of maize varieties and that this results in a degree of Striga resistance.

We have elucidated the entire biosynthetic pathway of all SLs in maize and we showed that the difference in strigolactone composition is the result of a difference in the expression of one of the genes in the pathway.

The line with the strongest reduction in the expression of this gene, a North-American cultivar, displays almost full Striga resistance compared with a susceptible control.

In collaboration with the CGIAR institute CIMMYT, we propose to create knock-out lines in this gene in two elite African maize varieties to deliver the proof-of-concept that this Striga resistance can be introduced into Africa.